1. Field of the Invention
This invention relates to programmable power supplies and, more specifically, to a programmable step down DC-DC converter controller.
2. Related Art
The microprocessor has evolved from an integrated semiconductor chip that controls only simple functions to rival the computing power of a mainframe computer. That evolution has brought ever increasing numbers of transistors integrated onto a single chip. For example, the current Intel Pentium.RTM. microprocessor chip has well over 5 million transistors. To achieve this density, the size of each transistor has been reduced to the sub-micron level; with each successive design geometry reduction, the corresponding maximum voltage at which the transistor operates has been reduced as well. This changing maximum operating voltage for microprocessors has led to the need for a programmable power supply such that with each successive change in voltage requirement for the microprocessor, the computer system designer does not have to completely re-engineer the associated power supply system. The voltage requirements of the microprocessor has been trending downwards over approximately the past 5 years, from 5 volts for the 386 and 486microprocessors, to 3.3 volts for the Pentium, and now to down to 3.1 volts for the Pentium Pro.RTM.. Operating voltages for microprocessors in 1997 will likely be in the range of 2.5 volts.
Previous generations of DC-DC (direct current-direct current) converter controllers provide fixed output voltages or, in some cases, are adjustable by changing a set of external resistors. In the production environment for personal computers, the microprocessor circuit board (also known as a "motherboard") therefore has had to be redesigned each time the operating voltage has been changed by the microprocessor manufacturer. To address the problems caused by the changing voltage requirements, Intel has programmed a voltage identification code (VID) into the Pentium Pro which can be read by a motherboard that has the appropriate capability. The motherboard, if it has the function built-in, then supplies the voltage identified by the VID to the microprocessor. This eliminates the requirement of the system designer to redesign the motherboard each time the microprocessor voltage changes because the microprocessor signals its own required voltage and the controller then automatically supplies the required voltage.
What is needed is a DC-DC converter controller designed with the ability to be programmed to address the changing power supply voltage needs for future lower voltage microprocessors. The DC-DC converter controller must be able to read the VID code programmed into the microprocessor and then supply the voltage called for by the microprocessor VID code.